The proposed research builds on exciting findings from the research conducted during the current period of funding. Our existing Program Project (PPG;P01 HL47540), now beginning its 16* year of funding, focuses on the role of psychosocial factors in the development of hypertension (HT) and cardiovascular disease (CVD). It comprises a body of work that has been supported continuously by NHLBI since 1988 (originally an R01), conducted by a well-established, multidisciplinary group of investigators at the Columbia University Medical Center (CUMC) and Stony Brook University. We have identified "Masked Hypertension," (MHT) the condition in which one has normal clinic blood pressure (BP) but an average daytime ambulatory BP above the threshold for hypertension. Although MHT is not diagnosed by conventional BP measurement criteria, it is associated, cross-sectionally, with increased target organ damage. We believe MHT to be of great clinical, etiological, and public health significance, as it is likely a highly prevalent condition, present in as many as 20 million Americans. The proposed PPG will investigate the contribution of MHT to la) future increases in blood pressure (BP) and lb) progression of target organ damage (Project 1, a prospective cohort study), 2) the psychophysiological mechanism(s) associated with MHT (Project 2, a psychophysiology laboratory reactivity/recovery mechanistic study), and 3) strategies to improve the diagnosis of hypertension in a costeffective manner (Project 3, a decision science study). This research program is crucial if those with MHT are to be cost-effectively identified for further monitoring and/or treatment, and if we are to understand MHT's mechanisms and clinical sequelae. Participants in our current MHT Study will be followed prospectively, with some being recruited to also participate in Project 2. Participants for Project 3 will be recruited from the general population and the primary care clinics of CUMC. They will constitute a new sample, over-sampling those with pre-hypertension or untreated Stage 1 hypertension by clinical BP criteria. This proposed P01 will address the NHLBI aims and goals by substantially increasing our understanding of the clinical sequelae of MHT and the mechanisms underlying this condition, and by applying a decision science approach to the development of a substantially improved algorithm for diagnosing hypertension and identifying those who are most likely to benefit from treatment. We believe that our findings are likely to have a major impact on the methods used to measure BP routinely in clinical practice.